#include <iostream>
using namespace std;

//Definition for singly-linked list.
struct ListNode {
    int val;
    ListNode *next;
    ListNode() : val(0), next(nullptr) {}
    ListNode(int x) : val(x), next(nullptr) {}
    ListNode(int x, ListNode *next) : val(x), next(next) {}
};

// class Solution {
// public:
//     ListNode* removeElements(ListNode* head, int val) {
//         // 删除头结点
//         while(head != NULL && head->val == val){
//             ListNode* tmp = head;
//             head = head->next;
//             delete tmp;
//         }

//         // 删除其他元素
//         ListNode* cur = head;
//         while(cur != NULL && cur->next != NULL){
//             if(cur->next->val == val){
//                 ListNode* tmp = cur->next;
//                 cur->next = cur->next->next;
//                 delete tmp;
//             }
//             else{
//                 cur = cur->next;
//             }
//         }
//         return head;
//     }
// };

// 虚拟头节点

class Solution {
public:
    ListNode* removeElements(ListNode* head, int val) {
        ListNode* dummyHead = new ListNode(0);
        dummyHead->next = head;
        ListNode* cur = dummyHead;
        while(cur->next != NULL){
            if(cur->next->val == val){
                ListNode* tmp = cur->next;
                cur->next = cur->next->next;
                delete tmp;
            }
            else{
                cur = cur->next;
            }
        }
        head = dummyHead->next;
        delete dummyHead;
        return head;
    }
};